Put the summary of the bug you're having here

What I expected to happen was...:
When I try to break the top half of a powered, extended piston it will break the whole piston/not break

What actually happened was...:
When I broke the top half of the piston, it only broke the top half and not the bottom half (Registering as 2 different blocks)
After breaking the arm it is no longer there, you can place blocks and walk through it
After you break the piston's arm, if you unpower the piston the arm will reappear and retract even retracting through non-piston moveable blocks

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. Place a piston
3. Power it
4. Break the arm of the piston
5. See the bug/glitch